Radio frequency (RF) spectrum is a scarce commodity for communications systems. Developing new communication systems is often hampered by the difficulty in allocating spectrum. A frustrating fact for the industry is that there is a lot of spectrum that exists that is only partially used because service providers with spectrum licenses do not provide (or need to provide) ubiquitous coverage. The Federal Communication Commission (FCC) of the United States has recently challenged the industry to find ways for communication systems to share the existing spectrum without impacting the each other. The difficulty of spectrum sharing is in finding ways for a secondary user (i.e., one that is not licensed to use the spectrum) to use the spectrum without interfering with the spectrum's licensee. Therefore a need exists for a method and apparatus for channel sharing between multiple communication systems in order to allow users of one communication system to use partially used spectrum from another communication system.